This section provides background information related to the present disclosure which is not necessarily prior art.
Additive manufacturing (AM) fabrication methods are proliferating rapidly, with photopolymer-based approaches comprising some of the most prominent methods. These stereolithographic techniques provide a useful balance of resolution, build speed, process control, and capital cost. However, these system metrics typically must be traded off one against another. Resolving the speed limitations, surface roughness (stair-step artifacts), and requirements for support structures will provide the next major steps forward in the progress of these technologies.
As additive manufacturing (AM) technologies gain prominence and versatility, one constraint on nearly every AM approach is the reliance on serially repeating low-dimensional unit operations, building structures up voxel-by-voxel, or layer-by-layer. This can be an advantage, yielding significant process flexibility, but is often a shortcoming, imposing deficiencies in surface finish and dimensional limitations; for instance, it is impossible to produce smoothly curving geometries. A few approaches have demonstrated the capability to generate 3D structures without requiring planar slicing, notably Hughes Research Laboratories' fabrication of lattices via latticed light-beams (see, T. A. Schaedler et al., “Ultralight Metallic Microlattices,” Science, Vol. 334, No. 6058, pp. 962-965, November 2011) and photonic crystals produced by interference lithography (see, Y. Lin, A. Harb, K. Lozano, D. Xu, and K. P. Chen, “Five beam holographic lithography for simultaneous fabrication of three dimensional photonic crystal templates and line defects using phase tunable diffractive optical element,” Opt. Express, Vol. 17, No. 19, p. 16625, September 2009.). However, these approaches are limited to periodic structures, with one of the dimensions substantially smaller than two others. Even Carbon3D's “continuous” liquid interface process (see, J. R. Tumbleston et al., “Continuous liquid interface production of 3D objects,” Science, Vol. 347, No. 6228, pp. 1349-1352, March 2015) still requires sequential fabrication based on 2D discretization.
Expanding the AM technology base to include fabrication by means of 3-D unit operations, which generate 3D shapes with arbitrary geometry (“volume at once”) is highly desirable. Such approaches are in their infancy: the first “volume-at-once” photopolymer-based fabrication was recently demonstrated as noted in M. Shusteff et al., “Additive Fabrication of 3D Structures by Holographic Lithography,” in Proceedings of the 26th Annual International Solid Freeform Fabrication Symposium, Austin, Tex., 2016, pp. 1183-1192. This approach used a holographically-shaped light field generated by a phase-only liquid crystal on silicon (LCoS) spatial light modulator (SLM). The geometries achievable by the Shusteff et al., approach are limited due to having constant cross-section along each of three orthogonal directions. This limitation arises largely from the small diffractive angles available from state of the art SLMs owing to their relatively large pixel size (minimum approximately 4 μm, but more typically 8 μm or larger).